1. Field of the Invention
This invention is concerned with a camera equipped with a data display function in which the data display function is designed so that several light emitting elements are driven concurrently with the scrolling of the film through the camera, enabling the display of data characters on the film.
2. Description of Related Art
Heretofore, cameras equipped with a data display function, in which several light emitting elements (such as LEDs) are driven concurrently with the scrolling of the film in order to display data characters on the film in dot matrix form, use an encoder to produce a signal concurrent with the scrolling of the film through the camera in order to provide timing for the data display.
The encoder includes opaque parts and transparent parts provided alternately in a radial direction at specified angular intervals on the encoder, which is rotatable. A photo-interrupter, through which the encoder rotates, detects these transparent and opaque parts, thereby causing the generation of pulses.
In order to make the camera smaller, it is necessary to make this encoder smaller. However, due to the limited sensitivity of the photo-interrupter, it is necessary to form the opaque parts and the transparent parts with a certain minimum width. Accordingly, in making the encoder smaller, it has been impossible to increase the number of opaque and transparent parts above a certain level. Additionally, the minimum tolerable width of opaque parts is different from the minimum tolerable width of the transparent parts. Accordingly, when the maximum number of opaque and transparent parts are provided on an encoder (by using the different minimum widths for the opaque and transparent parts), the pulses produced from the opaque parts have a different pulse width than the pulses produced from the transparent parts. This results in a non-uniform pulse signal being output by the photo-interrupter. The disadvantages of such a signal are detailed as follows.
In order to achieve proper timing for the display of characters in dot matrix form during the scrolling of the film, it is necessary to have a large number of pulses (such as, for example, 360 pulses) for each frame of the film. Generally, this is due to the size of the view screen and the characters being displayed. As a result, proper timing for the data display has been achieved by using signals (i.e., pulses) produced from both the opaque parts and the transparent parts of the encoder. In other words, both the front and the back edges, which result from the transition between transparent/opaque parts and opaque/transparent parts, of the pulse signal are used. Alternatively, depending on the size of the view screen, the duration (a) of a pulse is measured, and the interval a/2 is used for time control.
However, due to the dispersed arrangement of the photo-interrupter, the linkage of it to the encoder and various tolerance errors in the installation of the various parts, it is difficult to ensure that the detection time of the opaque parts and of the transparent parts will be consistent on the encoder. This makes it impossible to obtain a set time interval for all of the pulse time intervals (b) produced from the opaque parts and the pulse time intervals (a) produced from the transparent parts.
Accordingly, for the pulse time being measured, when the pulse time interval (a) of pulses produced from the transparent parts is measured, and when it differs from the pulse time interval (b) of pulses produced from the opaque parts, the data characters are not positioned in the middle of the time interval (b) pulses when using the time a/2 for time control, so that either the front or back dots of a character are shifted. As a result, the shape of each character differs when several characters are displayed, making it difficult to read the display. This has been especially true when the same character was repeatedly displayed.
FIG. 7 illustrates this problem, which is associated with conventional display procedures. The pulse signal 81 is produced by the photo-interrupter as the encoder rotates through it. The pulses having time duration (a) are produced when the transparent parts of the encoder pass through the photo-interrupter. The pulses having the time duration (b) are produced when the opaque parts of the encoder pass through the photo-interrupter. As can be seen from FIG. 7, the pulses produced from the opaque parts have a longer duration than the pulses produced from the transparent parts. Accordingly, when the boundaries or edges between pulses are used to trigger or otherwise control dot formation and when a second dot is formed at a time period a/2 after formation of the dot produced from the pulse edge, gaps are formed in the resulting characters because b.noteq.a. Moreover, in conventional cameras, this gap can be located at different portions of different characters. For example, referring to FIG. 7, the gap is located between the second and third columns of dots in the first, fifth and sixth characters; between the third and fourth columns of dots in the second character; and between the fourth and fifth columns of dots in the third and fourth characters. This non-uniformity in the shapes of the characters makes them difficult to read.